Multi-electrode cold-cathode discharge tube comprising ring magnet with attached electrodes



Apnl 11. 1967 D. REANEY 3,313,973

MULTI-ELECTRODE COLD-CATHODE DISCHARGE TUBE COMPRISING RING MAGNET WITH ATTACHED ELECTRODES Filed May 20, 1963 United States Patent 3,313,973 MULTI-ELECTRODE COLD-CATHODE DIS- CHARGE TUBE COMPRISING RING MAG- NET WITH ATTACHED ELECTRODES Donald Reaney, Long Eaton, England, assignoito Ericsson Telephones Limited, London, England, a British company Filed May 20, 1963, Ser. No. 282,534 Claims priority, application Great Britain, June 1, 1962, 21,131/ 62 1 Claim. (Cl. 313-161) The present invention relates to an improved multielectrode cold-cathode discharge tube.

Cold-cathode discharge tubes are well known which comprise a single anode electrode surrounded by a ring of cathode electrodes, usually ten in number. Between each pair of adjacent cathode electrodes are two or three guide electrodes ,provided to enable a discharge between the anode and one cathode to be transferred to an adjacent cathode. The guide electrodes are connected together to form common first guide, second guide, and possibly third guide connections, and the anode and each cathode is connected to a separate pin on the base of the tube. Such tubes may be used for selecting, counting and other purposes and are sold under the Registered Trade Mark Dekatron.

The operation of a tube of the type described above depends upon the relative potentials applied to the invested cat-hode and adjacent guide electrodes. The discharge is attracted away from a cathode by reducing the potential applied to an adjacent guide electrode below the potential of the cathode itself. By reducing the potentials'on two or three guide electrodes sequentially it is possible to move the discharge from one cathode to another. This operation by means of guide electrodes provides the tube with a particular determinable transfer characteristic. It is well known that during the operation of such a tube material is removed from the surface of the cathode electrodes by sputtering. A considerable proportion of the sputtered material is deposited on adjacent guide electrodes and changes the transfer characteristic of the tube. This is especially noticeable if the discharge is allowed to remain on one cathode for any length of time.

According to the present invention we provide a multielectrode cold-cathode discharge tube in which a dis-- charge investing a first electrode and one of a plurality of second electrodes arranged equidistant from the first electrode is capable of movement from one to another of the second electrodes under the influence of a uniform deflecting field perpendicular to that existing between the two invested electrodes, and in which such movement may be prevented by the application of a locking potential to a similar plurality of intermediate electrodes located one between each pair of adjacent second electrodes.

In a preferred embodiment the second and intermediate electrodes are arranged in a circle having the first electrode at its centre.

The invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIGURE 1 shows a sectional plan view of a tube according to one embodiment of the invention in which the deflecting field is provided by a cylindrical permanent magnet;

FIGURE 1a shows a modification of FIGURE 1 using an electromagnet;

FIGURE 2 shows, diagrammatically, a method of connection of the tube of FIGURE 1; and

FIGURE 3 shows a sectional plan view of a tube according to a further embodiment of the invention in which the deflecting field is an electrostatic field.

Referring now to FIGURE 1 a discharge tube 10 comprises a cylindrical glass envelope 11 having a disc or rod-shaped cathode C mounted substantially at its centre. Arranged in a concentric circle are ten anode electrodes A1 to A0 and ten locking electrodes L1 and L0, arranged alternately as shown. These electrodes are normally all connected to separate pins in the base of the tube, though the ten locking electrodes may be connected together to a single pin. The glass envelope is evacuated and filled with a hydrogen or hydrogen-inert gas mixture in known manner.

Around the outside of the envelope 11 is cemented a cylindrical permanent magnet 12 which is magnetised so as to produce a magnetic field parallel to the axes of the electrodes.

Referring now to FIGURE 2, the cathode electrode is connected through a resistor 13 to a source of negative potential of -500 volts. Each anode is connected through a separate resistor 21 to 30 to earth potential. Outputs S1 to S0 may be taken from the anode electrodes. The ten locking electrodes are connected together either inside or outside the tube to a control circuit (not shown). This normally applies a locking potential of the order of -180 volts to the locking electrodes.

With the tube connected as described a discharge will form between the cathode and one anode electrode. The magnetic field will tend to move the discharge around the tube in a direction depending upon the direction of the field, and this effect will be opposed by the electric field due to the locking potential. Thus the discharge will remain stationary until the locking potential is reduced. The control circuit when triggered, applies a 30 volt positive pulse to the locking electrodes and thus reduce the locking potential to volts. The discharge now moves around the tube to an adjacent anode electrode under the influence of the magnetic field. The duration of the control pulse is such that the discharge is only allowed to move one step around the tube.

If the locking potential is reduced or removed for any length of time the discharge will rotate freely around the tube, moving from one anode to the next. The freerunning speed depends upon several factors including the characteristics of the gas filling and the strengths of the electric and magnetic fields. The strength and location of the magnetic field are not critical, though there is an upper limit to the magnetic field strength above which the locking electrode will be ineffective With the applied potentials as shown in FIGURE 2 and a cathode current of two milliamps the output potential on an invested anode will be about -10 volts.

Although the above embodiment described the use of a cylindrical permanent magnet placed outside the envelope it is of course possible to place this magnet inside the envelope as shown in FIG. 1a. The cylindrical magnet in either position may be replaced by two or more separate magnets suitably located and magnetised. If ceramic magnets are used it is possible to incorporate some or all of the electrodes with the magnets by the use of conductive coatings.

In order to obtain an easily reversed direction of rotation the permanent magnetic field may be replaced by an electromagnetic field, the electromagnet having a hollow cylindrical core of the same shape as magnet 12 and embraced by an energizing winding 31. In such a case the direction of rotation may be reversed simply by reversing the energising current.

Patented Apr. 11, 1967 In the second embodiment of the invention the deflecting field is produced electrostatically. Referring to FIG- URE 3 it will be seen that the construction of the tube is very similar to that shown in FIGURE 1. The external magnet has been removed and a concentric ring of bias electrodes B1 to B20 has been added outside the ring of anodes and locking electrodes. The bias electrodes are located midway between each adjacent electrode already mentioned. The bias electrodes are either connected to separate pins in the base of the tube or alternate bias electrodes may be connected together and two bias connections taken to pins.

In operation the two sets of bias electrodes are connected to two sources of potential through a device which enables these two potentials to be readily reversed. A bistable circuit is suitable for this purpose, one bias connection being connected to each of the outputs. The potentials on the two sets of bias electrodes may be reversed by changing the state of the bistable device. The electric fields set up between adjacent bias electrodes are substantially tangential to the circles of electrodes.

The discharge formed between the cathode and one anode will tend to move to an adjacent anode under the influence of the local electrostatic field. This movement is prevented by the locking potential applied to the looking electrodes. When it is desired to move the discharge the locking potential is removed or reduced for sufficient time for the discharge to move to the adjacent anode.

The direction of rotation of the discharge will depend upon the direction of the local electrostatic field.

In order that the discharge shall continue to rotate around the anode in the same direction it is necessary to reverse the bias potentials after each step. Thus the tube control circuit is arranged to reduce or remove the locking potential and change the state of the bistable bias circuit each time an input signal is received.

If it is desired to reverse the direction of rotation of the discharge it is only necessary to put the bistable circuit out of step by applying an extra pulse to it. This will change the state of the bistable circuit Without reducing the locking potential.

With the potentials shown in FIGURE 1 the potential applied to the first set of bias electrodes should be about 1( volts and that applied to the second set of bias electrodes should be about 50 volts.

It is, of course, possible to produce the required electric fields by means other than the use of the electrodes described. Similarly it is not necessary to use a bistable device to reverse the bias potentials.

' Although the electrodes are shown as being of circular cross-section, this need not necessarily be the case.

The potentials applied to the various electrodes of the tube are only examples of suitable values, and other values may be used as required. The anode line is main- 4 tained at earth potential to avoid the problem of insulating the output leads. It is of course possible to connect the cathode resistor to earth and to apply a positive potential of 500 volts to the anode line. The difference between these and the other potentials would be maintained.

The embodiments described above are ten position tubes with ten anodes and ten locking electrodes. It is possible to vary this number as required so long as there are equal numbers of anodes and locking electrodes. If bias electrodes are used the number of these should also be equal to twice the number of anodes.

Both of the embodiments described above incorporate a single cathode electrode and a plurality of anode electrodes. A tube having a common anode and a plurality of cathodes will function in a similar way through the applied potentials will, of course, be different.

Although in the embodiments described above all the electrodes are arranged parallel to each other, they may be arranged otherwise. For example the outer electrodes may be arranged in the same plane pointing inwards towards the central electrode.

I claim:

A multi-electrode cold-cathode gas-filled discharge tube which includes a first electrode and a plurality of second electrodes disposed equidistant therefrom so that a discharge may invest the first electrode and any one of the second electrodes, at least one permanent magnet located inside the envelope of the tube and arranged to apply a uniform magnetic deflection field at right angles to a discharge so that the discharge is thereby deflected from one to another of said second electrodes, and an intermediate electrode between each pair of second electrodes capable of being maintained at a locking potential whereby deflection of a discharge is prevented, each of said second and said intermediate electrodes being carried by said magnet.

References Cited by the Examiner UNITED STATES PATENTS 2,846,611 8/1958 Hough et al 3l5-84.6 X 2,999,183 9/1951 Glaser 3158.5 3,008,067 11/1961 Somlyody 3158.5 X 3,028,520 4/1962 Wolfe et a1. 3l5-8.5 3,085,174 4/1963 Van Tol et al. 31584.6 X 3,092,752 6/1963 Wolfe 3158.5 3,168,674 2/1965 Somlyody 3158.5 3,226,591 12/1965 Josephson 31316l X FOREIGN PATENTS 697,602 9/ 1953 Great Britain.

JAMES W. LAWRENCE, Primary Examiner.

ROBERT SEGAL, Assistant Examiner. 

